Previous murine models of blastomycosis have relied on infection of mice with the yeast form of Blastomyces dermatitidis. These models have the inherent weakness of bypassing the conidium, the infectious particle found in the environment. As a result, the crucial events that determine the host response to inhaled conidia and the mechanism of transformation of conidia to yeast form thereby causing progressive infection are left unstudied. This proposal will address this aspect of the pathogenesis of murine pulmonary blastomycosis by combining in vivo and in vitro investigations with B. dermatitidis derived conidia as the infectious fungus particle. Three major specific aims constitute the basis of this application: 1) A mouse model of pulmonary blastomycosis will be developed and characterized using conidia derived from various strains of B. dermatitidis to infect mice by the intranasal route. Since the yeast forms of these strains have been well described by other investigators, comparisons of the in vivo behavior of conidia and yeasts from a single strain can then be made, permitting the identification of virulence factors associated with either of the morphologic forms; 2) The in vitro effects of murine bronchoalveolar macrophages on conidia will be assessed in 2 different assays of killing of the fungus. Since the cellular response to inhaled conidia has not been characterized, serial lung lavage of infected mice will be done to help guide the direction of these studies. Should neutrophils be found in large numbers in the lungs following inhalation of conidia, studies will be expanded to evaluate the in vitro activity of neutrophils against conidia; and 3) The activity of toxic products derived from effector cells including products of oxidative metabolism and nonoxidative mechanisms of host defense derived from bronchoalveolar macrophage and neutrophil granules will be isolated and evaluated using conidia and yeast forms derived from the different strains of B. dermatitidis as targets. The CTLs derived granules obtained from Dr. E. Podack will be included as part of the studies with nonoxidative killing mechanisms. Comparisons with and extensions of previous data that we have generated with yeast forms will be made. The results of these studies should permit the formulation of comprehensive hypotheses regarding the pathogenesis of murine blastomycosis.